Skin integrity is of importance for the protection and separation of body tissues from the surrounding environment. The loss of skin due to burns or trauma exposes the body to severe stress, impairing or even eliminating the many vital functions this organ performs. The skin contains two main layers of cells: a thin outer layer, the epidermis, and a thicker inner layer, the dermis. Full thickness skin tissue is comprised of keratinocytes lined on a basement membrane, produced by fibroblasts. Deeper layers of the skin include, in addition to fibroblasts, fat cells and multiple subsets of immune cells such as dendritic cells, lymphocytes and polymorphonuclear cells. The complex organization of normal skin is designed to support the numerous functions of this organ as both an immunologic and a physical barrier. Nevertheless, not much is known about the factors responsible for the complex architecture of this organ under physiologic and pathologic conditions.
Chemokines and Chemokine Inhibitors
Cytokines are, generally, small protein or polypeptide-based molecules that modulate the activity of certain cell types following binding to cell surface receptors. Chemokines are a subgroup of cytokines that mediate a range of proinflammatory effects on leukocytes, such as chemotaxis, degranulation, and integrin activation. The CXC chemokines are a group of chemokines so named due to the conserved Cys-Xaa-Cys sequence element located towards their N-terminus. Among this group of chemokines is stromal-derived factor-1 (SDF-1, also known as CXCL12).
CXCL12 controls many aspects of stem cell function. CXCL12 has been identified as a powerful chemoattractant for immature hematopoietic stem cells (Aiuti et al., 1997). Mice that lack either CXCL12 or its receptor CXCR4 exhibit many defects, including impaired hematopoiesis in the fetal bone marrow (Nagasawa et al., 1996; Zou et al., 1998). Recently, it was shown that mobilization, homing and engraftment of hematopoietic stem cells as well as the trafficking of neuronal and primordial germ cells is dependent on the expression of CXCL12 and CXCR4 (Peled et al., 1999). It was also shown that the expression of CXCL12 is upregulated following irradiation and hypoxia and that CXCL12 can induce the recruitment of endothelial progenitor cells in a regeneration model for myocardial infarction (Askari et al., 2003; Ceradini et al., 2004; Ponomaryov et al., 2000). The regulation of CXCL12 and its physiological role in peripheral tissue repair remain incompletely understood. A recent study showed that CXCL12 gene expression is regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1) in endothelial cells, resulting in the selective in vivo expression of CXCL12 in ischemic tissue in direct proportion to reduced oxygen tension (Hitchon et al., 2002; Schioppa et al., 2003). HIF-1-induced CXCL12 expression increases the adhesion, migration and homing of circulating CXCR4-positive progenitor cells to ischemic tissue. Other studies have shown that the von Hippel-Lindau tumor suppressor protein, pVHL, negatively regulates CXCR4 expression owing to its capacity to target HIF for degradation under normoxic conditions (Staller et al., 2003).
Thus, CXCL12 plays an important role in the organization of tissues during development and following irradiation and hypoxia. CXCL12 is expressed by dendritic cells, fibroblasts and endothelial cells in human skin (Pablos et al., 1999).
Various chemokine receptor inhibitors, including CXCR4 inhibitors, have been described in the art. For example, a bicyclam drug termed AMD3100, originally discovered as an anti-HIV compound and which specifically interacts with CXCR4, is currently undergoing clinical trials to evaluate its ability to increase stem cells available for transplant (Lack et al., 2005).
The involvement of chemokines in various aspects of leukocyte activity has prompted different speculations regarding the possibility of regulating wound healing by modulating chemokine activity. For instance, U.S. Patent Application Publication No. 2001/0006640 discloses peptides derived from various chemokines, which peptides are homologous to residues 46-67 or 27-45 of mature human MCP-1 and may act as antagonists or agonists of chemokine activity, and uses thereof for immunomodulation. Certain particular peptides derived from CXCL12 were disclosed in the specification. The '640 application further suggests that peptide chemokine inhibitors derived from chemokines such as MCP-1 and IL-8 may inhibit recruitment of neutrophil or macrophage accumulation at the site of the wound, and thereby enhance wound healing.
U.S. Patent Application Publication No. 2004/0209921 discloses heterocyclic compounds that bind to chemokine receptors, including CXCR4 and CCR5, which may possess protective effects against infection of target cells by a human immunodeficiency virus (HIV). Other potential uses for these compounds suggested by '921 are enhancing the population of progenitor and/or stem cells, stimulating the production of white blood cells, and/or effecting regeneration of cardiac tissue. The '921 application speculates that elevated white blood cell counts may be beneficial for wound healing.
T-140 Analogs
T-140 is a 14-residue synthetic peptide developed by some of the inventors of the present invention as a specific CXCR4 antagonist which suppress T-cell line-tropic HIV-1 (X4-HIV-1) entry through specific binding to CXCR4 (Tamamura et al., 1998). Subsequently, peptide analogs of T-140 were developed by some of the inventors of the present invention as specific CXCR4 antagonist peptides with inhibitory activity at nanomolar levels (see Tamamura et al., 2003, WO 2002/020561 and WO 2004/020462).
WO 2002/020561 discloses novel peptide analogs and derivatives of T-140. The '561 publication demonstrates that the claimed peptides are potent CXCR4 inhibitors, manifesting high anti-HIV virus activity and low cytotoxicity.
WO 2004/020462 discloses additional novel peptide analogs and derivatives of T-140. The '462 publication further discloses novel preventive and therapeutic compositions and methods of using same utilizing T-140 analogs for the treatment of cancer and chronic rheumatoid arthritis. The specification of '462 demonstrates the ability of these peptides to inhibit cancer cell migration, including breast cancer and leukemia cells, and to inhibit mastasis formation in vivo. Further demonstrated therein is inhibition of delayed-type hypersensitivity reaction in mice and collagen-induced arthritis, an animal model of rheumatoid arthritis.
None of the background art discloses or demonstrates that CXCR4 antagonists, particularly T-140 analogs, may be effectively used for the treatment of skin burns and for promoting wound healing while inhibiting fibrosis. There exists a need for improved treatments of skin lesions effective to promote the healing process of wounds and skin burns, and to prevent scar formation and other diseases associated with fibrosis.